cert.py 文件源码

def _rsassa_pss_sign(self, M, h=None, mgf=None, sLen=None):
        """
        Implements RSASSA-PSS-SIGN() function described in Sect. 8.1.1 of
        RFC 3447.

        Input:
           M: message to be signed, an octet string

        Output:
           signature, an octet string of length k, where k is the length in
           octets of the RSA modulus n.

        On error, None is returned.
        """

        # Set default parameters if not provided
        if h is None: # By default, sha1
            h = "sha1"
        if not h in _hashFuncParams:
            warning("Key._rsassa_pss_sign(): unknown hash function "
                    "provided (%s)" % h)
            return None
        if mgf is None: # use mgf1 with underlying hash function
            mgf = lambda x,y: pkcs_mgf1(x, y, h)
        if sLen is None: # use Hash output length (A.2.3 of RFC 3447)
            hLen = _hashFuncParams[h][0]
            sLen = hLen

        # 1) EMSA-PSS encoding
        modBits = self.modulusLen
        k = modBits / 8
        EM = pkcs_emsa_pss_encode(M, modBits - 1, h, mgf, sLen)
        if EM is None:
            warning("Key._rsassa_pss_sign(): unable to encode")
            return None

        # 2) RSA signature
        m = pkcs_os2ip(EM)                          # 2.a)
        s = self._rsasp1(m)                         # 2.b)
        S = pkcs_i2osp(s, k)                        # 2.c)

        return S                                    # 3)